WASHINGTON (Reuters) - Nearly a dozen U.S. states and Washington D.C. on Tuesday promised to defend federal automobile efficiency standards against a rollback proposed this week by Scott Pruitt, the embattled head of the Environmental Protection Agency.

"All Americans ... deserve to enjoy fuel-efficient, low-emission cars and light trucks that save money on gas, improve our health and support American jobs," the attorneys general from 11 states said in a statement responding to Pruitt's proposal on Monday to ease the Obama-era standards.

The standards called for roughly doubling by 2025 the average fuel efficiency of new vehicles sold in the United States to about 50 miles (80 km) per gallon. Proponents say they help spur innovation in clean technologies and cut emissions of the greenhouse gas carbon dioxide.

California has long been allowed by an EPA waiver to impose stricter standards than Washington does on vehicle emissions of some pollutants. And 12 other states follow California's lead on cleaner cars.

The attorneys general, from states including New York, Iowa and Massachusetts, said they would challenge a rollback in court. California Attorney General Xavier Becerra has already threatened to sue in defense of the standards.

The statement, also signed by more than 50 mayors from around the country, said automakers have been making progress in meeting the national standards and that compliance costs have been lower than projected.

Auto industry executives have not publicly sought specific reductions in the requirements negotiated with the Obama administration in 2011 as part of a bailout deal. But they have urged Pruitt and President Donald Trump to revise the standards so it becomes easier and less costly to meet the targets.

Pruitt defended his decision at EPA headquarters on Tuesday.

"We have nothing to be apologetic about with respect to the progress we've made in reducing emissions as a country," Pruitt said. The EPA will make sure that U.S. consumers would not have to buy more expensive autos as a result of efficiency standards, he said.

Pruitt, a former attorney general of Oklahoma, a major oil producer, has been criticized by politicians after reports that he paid well below market rates to live in a condo owned by a lobbyist who deals with issues overseen by his agency. Trump and White House Chief of Staff John Kelly phoned Pruitt this week to say they support him, an administration source said on Tuesday.

(Reporting by Timothy Gardner and Richard Valdmanis; Editing by James Dalgleish and Richard Chang)